Carbon electrode for an arc lamp

ABSTRACT

A carbon electrode for an arc lamp used as a light source for apparatus for measuring fading and weathering of such materials as paints and fabrics. The electrode is a carbon electrode bar coated with aluminum or an aluminum alloy on all the peripheral surface thereof except the discharge tip. The electrode bar can be further coated with a film of aluminum oxide or silicon oxide other than at the discharge tip and the electrode holding section.

United States Patent 11 1 1111 3,867,667

Suga 1451 Feb. 18, 1975 CARBON ELECTRODE FOR AN ARC LAMP Primar Examiner-R. N. Envall Jr.

76 1 t Sh s Y y 1 men or 'ff y:%' g 2 Attorney, Agent, or Firm-Wenderoth, Lmd & Ponack PP bio-1448349 A carbon electrode for an arc lamp used as a light source for apparatus for measuring fading and weath- 52 us. 01. 314/60, 13/18 hiring of Such materials as Paints and fabrics- The elec- [51] 1m. (:1. H05b 31/06 is a Carbon electrode bar coated with aluminum 58 Field 61 Search 13/18; 314/60; 313/355; or an aluminum alloy the Peripheral Surface 219/146 thereof except the discharge tip. The electrode bar can be further coated with a film of aluminum oxide 5 References Cited or silicon oxide other than at the discharge tip and the UNITED STATES PATENTS electrode holding section. 3,348,929 10/1967 Valtschev et al. 13/18 x 1 Claim, 12 wing Figures get PATENIH] FEB I 8 I975 SHEET 2 [IF 2 WAVELENGTH (nm) FIG.5CL

WAVELENGTH (nm FIGSI) WAVELENGTH (nm CARBON ELECTRODE FOR AN ARC LAMP BACKGROUND AND BRIEF DESCRIPTION OF THE INVENTION This invention relates to a carbon electrode for an arc lamp used in fading or weathering tests of materials such as paints or fabrics.

A sunshine carbon arc lamp used for fading and weathering meters is shown in FIG. I, and an ultraviolet carbon arc lamp used for such meters is shown in FIG. 2. The ultra-violet arc lamp is intended chiefly to produce ultra-violet light, and has an upper carbon electrode u and a lower carbon electrode 1, both of which are uncoated. The conventional carbon electrode used with such ultra-violet arc lamps consists merely of a cored or a non-cored carbon electrode bar as shown in FIGS. 3b and 3a. They are adapted to discharge the current in a satisfactorily sealed glass globe g. The arc lamp is kept in a state of stable luminance over a prolonged combustion period. If the globe is not sealed tightly, the combustion may proceed too rapidly, and a large amount of infra-red radiation may be omitted on account of high temperature of the electrode. The sunshine carbon arc lamp is fitted with a ventilating blower for removing the cinders and exhaust gases produced by the current discharge The carbon electrode I used with this are lamp, as shown in FIG. 3c, is usually coated with copper 4 on all of its peripheral surface except the discharge tip to reduce the heating of the electrode, but toxic copper fumes or copper oxide may be produced and be present in the exhausted gas. In addition the thickness of the film can not be controlled so as to be uniform because the copper film is usually deposited on the carbon electrode by plating or a similar operation.

The object of this invention is to obviate the above defects inherent in the conventional carbon electrodes and to provide a carbon electrode for use with carbon arc lamps and comprising a carbon electrode bar coated with aluminum or aluminum alloy on all the peripheral surface thereof except the discharge tip, and which can further be coated with a film of aluminum oxide or silicon oxide on the peripheral surface thereof other than said discharge tip and the electrode holding portion, whereby carbon consumption can be reduced and the carbon electrode will produce a satisfactory spectrum of radiations for fading or weathering tests.

BRIEF DESCRIPTION OF THE FIGURES This invention will now be described by referring to an embodiment thereof shown in the accompanying drawings, in which:

FIG. 1 is a diagrammatic elevation view of the structure of a sunshine arc lamp;

FIG. 2 is a similar view of an ultra-violet arc lamp;

FIG. 3a-3a are sectional views of conventional carbon electrodes;

FIG. 4a-4d are sectional views of the carbon electrodes of the present invention;

FIGS. 5a and 5b are graphs showing the spectrum of an arc lamp using the ultraviolet carbon electrode according to the invention coated with aluminum or aluminum alloy film, FIG. 5a showing the ultra-violet and visible light ranges and FIG. 5b showing the infra-red range with the energy value magnified by times to make the energy value in said range more apparent; and

FIG. 6 is a graph showing the spectrum of an arc lamp using the dual coated sunshine carbon electrode according to the invention.

DETAILED DESCRIPTION OF THE INVENTION The carbon electrode of this invention for use with carbon arc lamps consists of a carbon electrode bar 10 coated with a coating I of aluminum or an alloy predominantly of aluminum on all the peripheral surface thereof except the discharge tip. The electrode bar can be uncored as in FIG. 4a or cored as in FIG. 4b. Ac cording to a modification, the aluminum or aluminum alloy coating on the electrode bar can be further coated with a coating of aluminum oxide or silicon oxide 3 on the surfaces other than the electrode holding portion 2. The electrode bar can be cored as in FIG. 4c or uncored as in FIG. 4d. The aluminum or aluminum alloy coatings can be deposited by any convenient method, as for instance by spray ejecting molten metal with the aid of compressed air, or placing the aluminum or aluminum alloy coating around the carbon rod and bonding the coating to the rod with an electrically conductive adhesive, or metallizing metal particles under a vacuum. The aluminum oxide or silicon oxide film can also be deposited by any convenient method, as for instance by spray ejecting the aluminum or silicon with a plasma torch or an oxyacetylene torch.

The thickness of the aluminum and aluminum alloy coating, and the thickness of the aluminum oxide or silicon coating should be 0.05 0.5 mm. An example of the composition of the aluminum alloy is aluminum 99.85% silicon 0.15%.

Turning first to the carbon electrode consisting of a carbon bar coated with an aluminum or aluminum alloy coating, the discharge current flows through the aluminum or the aluminum alloy coating which has a smaller electrical resistance than the carbon, and the electrode itself will thus be heated to a minimum degree. Thus, when the lamp is kept lighted, due to the presence of the coating, the carbon rod will be subjected to less oxidation than an uncoated rod because it is protected from the ambient air, and the carbon consumption will be reduced accordingly.

FIGS. 5a and 5b show the spectrum of the luminous ultra-violet carbon electrode coated with aluminum or aluminum alloy. As seen from these FIGS., the energy value in the ultra-violet range known to cause the deterioration of the carbon electrode is about the same as that observed for a conventional ultra-violet carbon electrode, but the energy value in the infra-red range is lower than that observed for the conventional electrode. The radiation responsible for the deterioration of the test specimen in a fading and weathering test is the ultra-violet light, and the energy in the infra-red range has, in general, the effect of raising the temperature of the test specimen.

If the energy of the radiation in the infra-red wavelengths is low, the radiant heat received by the test specimen can be reduced, and the test can be conducted at a lower temperature, which is desirable because a higher energy in said radiation may cause excessively high temperatures and consequent inaccurate test results. For this reason, the carbon electrode according to this invention is highly suited for use as a light source in apparatus for conducting fading and weathering tests. In the spectrum of the sunshine carbon electrode, not shown, the energy emitted by the electrode in the ultra-violet range is about the same as that emitted by the conventional carbon electrode, but the energy emitted by the former electrode in the infrared range is generally low, and hence the electrode can be used advantageously as light source for fading or weathering tests. During light emission from the sunshine carbon arc lamp at the time of current discharge an air stream is passed over the electrode, thus resulting in dispersion of cinders and exhaust gases which are generated. With the conventional copper-coated carbon electrode, toxic copper fumes or copper oxide are apt to be produced and scattered in the ambient atmosphere. This situation can be avoided by the use of the present carbon electrode.

The carbon electrode further coated with aluminum oxide or silicon oxide has the same advantages as described in the foregoing, and also has an additional advantage that, as the discharge tip of the electrode is consumed during the current discharge and the aluminum coating is gradually heated and starts to melt, the melted aluminum metal will not be peeled from the carbon electrode immediately, but is combined with the aluminum oxide or silicon oxide, the melting points of which are higher than the melting point of the metallic aluminum, into a vitreous ceramic substance at the prevailing high temperature. The vitreous ceramic substance so formed is not scattered into the ambient air,

but descends gradually under the effect of gravity. In addition, any abnormal discharge from the side surfaces of the electrode can be avoided during the current discharge due to the elevated electrical resistance of the aluminum oxide. It has also been discovered that the life of an arc lamp using the carbon electrode according to the invention is increased by about percent over that of the arc lamp using a conventional electrode. It should also be mentioned that the exhaust gas is composed of non-toxic aluminum, aluminum oxide and silicon oxide, which is a great advantage in overcoming the problem of pollution.

FIG. 6 shows the spectrum of a sunshine arc lamp having the dual coated carbon electrode according to the invention. The spectrum of the ultra-violet part is about the same as that shown in FIG. 5a.

As described above, when used as light source in an apparatus for carrying out fading and weathering tests,

the car on electrode for are lamps according to this invention has the following advantages,

l. Owing to the lower electrical resistance of aluminum metal, the heatingof the electrode due to the discharge current is reduced, while insulation against the external heat is provided by the aluminum oxide or silicon oxide film, thus preventing carbon consumption caused by oxidation with ambient air, and increasing the time over which combustion takes place.

2. The reduced energy value in the infra-red range observed in the spectrum makes it possible to conduct fading or weathering tests at the desired lower temperatures.

3. The cinders formed by combustion consist mainly of nontoxic aluminum oxides and silicon oxides.

4. The emitted light is stable since the aluminum oxide and silicon oxide are nonconductive and the discharge occurs solely at the tip of the electrode.

5. The dispersion of aluminum metal and hence the contamination of the glass filter and reduction in its transmittance is avoided due to the dual coating on the carbon electrode, and the volume of light is kept constant during the test period.

What is claimed is:

l. A carbon electrode comprising:

a carbon electrode bar having at one end thereof a discharge tip and having at the other end thereof an electrode holding section;

a first coating on all the peripheral surfaces of said bar other than said discharge tip, said coating material being from the group consisting of aluminum and alloy consisting predominantly of aluminum; and

a second coating of material taken from the group consisting of aluminum oxide and silicon oxide coating all the peripheral surfaces of said bar other than said discharge tip and said electrode holding section. 

1. A CARBON ELECTRODE COMPRISING: A CARBON ELECTRODE BAR HAVING AT ONE END THEREOF A DISCHARGE TIP AND HAVING AT THE OTHER END THEREOF AN ELECTRODE HOLDING SECTION; A FIRST COATING ON ALL THE PERIPHERAL SURFACES OF SAID BAR OTHER THAN SAID DISCHARGE TIP, SAID COATING MATERIAL BEING FROM THE GROUP CONSISTING OF ALUMINUM AND ALLOY CONSISTING PREDOMINANTLY OF ALUMINUM; AND A SECOND COATING OF MATERIAL TAKEN FROM THE GROUP CONSISTING OF ALUMINUM OXIDE AND SILICON OXIDE COATING ALL THE 